Power control and user multiplexing for heterogeneous network coordinated multipoint operations

ABSTRACT

Certain aspects of the present disclosure relate to techniques for power control and user multiplexing for coordinated multi-point (CoMP) transmission and reception in heterogeneous networks (HetNet).

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

The present application is a divisional application of U.S. applicationSer. No. 13/372,458, entitled “POWER CONTROL AND USER MULTIPLEXING FORHETEROGENEOUS NETWORK COORDINATED MULTIPOINT OPERATIONS,” filed Feb. 13,2012, which claims priority to U.S. Provisional Application No.61/442,650, entitled “POWER CONTROL AND USER MULTIPLEXING HETNET COMP,”filed Feb. 14, 2011, all assigned to the assignee hereof andincorporated herein by reference.

BACKGROUND I. Field

Certain aspects of the disclosure generally relate to wirelesscommunications and, more particularly, to techniques for power controland user multiplexing for coordinated multi-point (CoMP) transmissionand reception in heterogeneous networks (HetNet).

II. Background

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. Examples of such multiple-access networks include CodeDivision Multiple Access (CDMA) networks, Time Division Multiple Access(TDMA) networks, Frequency Division Multiple Access (FDMA) networks,Orthogonal FDMA (OFDMA) networks and Single-Carrier FDMA (SC-FDMA)networks.

A wireless communication network may include a number of base stations(BS) that can support communication for a number of user equipments(UEs). A UE may communicate with a base station via the downlink anduplink. The downlink (or forward link) refers to the communication linkfrom the base station to the UE, and the uplink (or reverse link) refersto the communication link from the UE to the base station.

A base station may transmit data and control information on the downlinkto a UE and/or may receive data and control information on the uplinkfrom the UE. On the downlink, a transmission from the base station mayobserve interference due to transmissions from neighbor base stations.On the uplink, a transmission from the UE may cause interference totransmissions from other UEs communicating with the neighbor basestations. The interference may degrade performance on both the downlinkand uplink.

SUMMARY

In an aspect of the disclosure, a method for wireless communications isprovided.

Certain aspects of the present disclosure provide techniques forwireless communications by a user equipment (UE). The techniquesgenerally include measuring channel state information reference signals(CSI-RS) transmitted from at least one of a set of transmission pointsinvolved in coordinated multipoint (CoMP) operations with the UE andperforming open loop power control based on the measured CSI-RS from atleast one of the transmission points.

Certain aspects of the present disclosure provide techniques forwireless communications by a base station. The techniques includedetermining one or more parameters for use by a user equipment (UE) inopen loop (OL) power control, wherein the one or more parameters aredetermined to take into account coordinated multipoint (CoMP) operationsand signaling the one or more parameters to the UE.

Certain aspects of the present disclosure provide techniques forwireless communications by a base station. The techniques includereceiving a transmission from a UE and determining one or more cells toinclude in a coordinated multipoint (CoMP) group, based on the receivedtransmission.

Certain aspects of the present disclosure provide techniques forwireless communications by a user equipment. The techniques includereceiving distinct channel state information reference signals (CSI-RS)transmitted from a plurality of cells; and transmitting feedback, basedon the received CSI-RS, that may be used to determine one or more cellsto include in an uplink (UL) coordinated multipoint (CoMP) group.

Certain aspects of the present disclosure provide techniques forwireless communications by a base station. The techniques includedetermining a channel state information reference signal (CSI-RS), theCSI-RS being different from CSI-RS transmitted by one or more othertransmission points sharing a common physical cell identifier (PCI) withthe base station, the CSI-RS being decoupled from the PCI; andtransmitting the CSI-RS from the base station.

Certain aspects of the present disclosure provide techniques forwireless communications by a user equipment. The techniques includetransmitting a sounding reference signal (SRS) from the UE in proximityto a plurality of transmission points sharing a common physical cellidentifier (PCI); and receiving, from at least one of the transmissionpoints, information regarding configuration for uplink coordinatedmultipoint (UL CoMP) operation, the configuration being decoupled fromthe PCI.

Certain aspects of the present disclosure provide techniques forwireless communications by a transmission point involved in CoMPoperations. The techniques include signaling one or more UEs regarding achannel quality indication (CQI) configuration for CQI transmission,wherein the signaled CQI configuration is decoupled from physical cellidentifier (PCI) of the transmission point.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of awireless communications network in accordance with certain aspects ofthe present disclosure.

FIG. 2 is a block diagram conceptually illustrating an example of aframe structure in a wireless communications network in accordance withcertain aspects of the present disclosure.

FIG. 2A shows an example format for the uplink in Long Term Evolution(LTE) in accordance with certain aspects of the present disclosure.

FIG. 3 shows a block diagram conceptually illustrating an example of aNode B in communication with a user equipment device (UE) in a wirelesscommunications network in accordance with certain aspects of the presentdisclosure.

FIG. 4 illustrates an example heterogeneous network (HetNet) inaccordance with certain aspects of the present disclosure.

FIG. 5 illustrates example resource partitioning in a heterogeneousnetwork in accordance with certain aspects of the present disclosure.

FIG. 6 illustrates example cooperative partitioning of subframes in aheterogeneous network in accordance with certain aspects of the presentdisclosure.

FIG. 7 is a diagram illustrating a range expanded cellular region in aheterogeneous network.

FIG. 8 is a diagram illustrating a network with a macro eNB and remoteradio heads (RRHs) in accordance with certain aspects of the presentdisclosure.

FIG. 9 illustrates an example scenario for HetNet CoMP where only themacro cell transmits a common reference signal (CRS) in accordance withcertain aspects of the present disclosure.

FIG. 10 illustrates example operations 1000, performed at a basestation, for uplink power control, in accordance with certain aspects ofthe disclosure.

FIG. 10A illustrates example components capable of performing theoperations illustrated in FIG. 10 in accordance with certain aspects ofthe present disclosure.

FIG. 11 illustrates example operations, performed by a UE, for uplinkpower control to avoid jamming a close by RRH, in accordance withcertain aspects of the present disclosure.

FIG. 11A illustrates example components capable of performing theoperations illustrated in FIG. 11 in accordance with certain aspects ofthe present disclosure.

FIG. 12 illustrates an example scenario for HetNet CoMP where both macroand pico cells transmit a same CRS in accordance with certain aspects ofthe present disclosure.

FIG. 13 illustrates example operations, performed by a base station, forgrouping of cells associated with DL CoMP, in accordance with certainaspects of the present disclosure.

FIG. 13A illustrates example components capable of performing theoperations illustrated in FIG. 13 in accordance with certain aspects ofthe present disclosure.

FIG. 14 illustrates example operations, performed by a UE, for groupingof cells associated with UL CoMP, in accordance with certain aspects ofthe present disclosure

FIG. 14A illustrates example components capable of performing theoperations illustrated in FIG. 14 in accordance with certain aspects ofthe present disclosure

FIG. 15 illustrates example operations, performed by a UE, for groupingof cells associated with CoMP, in accordance with certain aspects of thepresent disclosure

FIG. 15A illustrates example components capable of performing theoperations illustrated in FIG. 15 in accordance with certain aspects ofthe present disclosure

FIG. 16 illustrates example operations, performed by a base station, forgrouping of cells associated with UL CoMP, in accordance with certainaspects of the present disclosure.

FIG. 16A illustrates example components capable of performing theoperations illustrated in FIG. 16 in accordance with certain aspects ofthe present disclosure

FIG. 17 illustrates example operations, by a transmission point involvedin CoMP operations, in accordance with certain aspects of the presentdisclosure

FIG. 17A illustrates example components capable of performing theoperations illustrated in FIG. 17 in accordance with certain aspects ofthe present disclosure

FIG. 18 illustrates example operations, by a transmission point involvedin CoMP operations, in accordance with certain aspects of the presentdisclosure

FIG. 18A illustrates example components capable of performing theoperations illustrated in FIG. 18 in accordance with certain aspects ofthe present disclosure

FIG. 19 illustrates example operations, performed by a UE involved inCoMP operations, in accordance with certain aspects of the presentdisclosure.

FIG. 19A illustrates example components capable of performing theoperations illustrated in FIG. 19 in accordance with certain aspects ofthe present disclosure

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. CDMA2000 coversIS-2000, IS-95, and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part ofUniversal Mobile Telecommunication System (UMTS). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS thatuse E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). CDMA2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the wireless networks andradio technologies mentioned above as well as other wireless networksand radio technologies. For clarity, certain aspects of the techniquesare described below for LTE, and LTE terminology is used in much of thedescription below.

Example Wireless Network

FIG. 1 shows a wireless communication network 100, which may be an LTEnetwork. The wireless network 100 may include a number of evolved NodeBs (eNBs) 110 and other network entities. An eNB may be a station thatcommunicates with user equipment devices (UEs) and may also be referredto as a base station, a Node B, an access point, etc. Each eNB 110 mayprovide communication coverage for a particular geographic area. In3GPP, the term “cell” can refer to a coverage area of an eNB and/or aneNB subsystem serving this coverage area, depending on the context inwhich the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a Closed Subscriber Group (CSG), UEs for users in the home,etc.). An eNB for a macro cell may be referred to as a macro eNB (i.e.,a macro base station). An eNB for a pico cell may be referred to as apico eNB (i.e., a pico base station). An eNB for a femto cell may bereferred to as a femto eNB (i.e., a femto base station) or a home eNB.In the example shown in FIG. 1, eNBs 110 a, 110 b, and 110 c may bemacro eNBs for macro cells 102 a, 102 b, and 102 c, respectively. eNB110 x may be a pico eNB for a pico cell 102 x. eNBs 110 y and 110 z maybe femto eNBs for femto cells 102 y and 102 z, respectively. An eNB maysupport one or multiple (e.g., three) cells.

The wireless network 100 may also include relay stations. A relaystation is a station that receives a transmission of data and/or otherinformation from an upstream station (e.g., an eNB or a UE) and sends atransmission of the data and/or other information to a downstreamstation (e.g., a UE or an eNB). A relay station may also be a UE thatrelays transmissions for other UEs. In the example shown in FIG. 1, arelay station 110 r may communicate with eNB 110 a and a UE 120 r inorder to facilitate communication between eNB 110 a and UE 120 r. Arelay station may also be referred to as a relay eNB, a relay, etc.

The wireless network 100 may be a heterogeneous network (HetNet) thatincludes eNBs of different types, e.g., macro eNBs, pico eNBs, femtoeNBs, relays, etc. These different types of eNBs may have differenttransmit power levels, different coverage areas, and different impact oninterference in the wireless network 100. For example, macro eNBs mayhave a high transmit power level (e.g., 20 watts) whereas pico eNBs,femto eNBs, and relays may have a lower transmit power level (e.g., 1watt).

The wireless network 100 may support synchronous or asynchronousoperation. For synchronous operation, the eNBs may have similar frametiming, and transmissions from different eNBs may be approximatelyaligned in time. For asynchronous operation, the eNBs may have differentframe timing, and transmissions from different eNBs may not be alignedin time. The techniques described herein may be used for bothsynchronous and asynchronous operation.

A network controller 130 may couple to a set of eNBs and providecoordination and control for these eNBs. The network controller 130 maycommunicate with eNBs 110 via a backhaul. The eNBs 110 may alsocommunicate with one another, e.g., directly or indirectly via wirelessor wireline backhaul.

The UEs 120 may be dispersed throughout the wireless network 100, andeach UE may be stationary or mobile. A UE may also be referred to as aterminal, a mobile station, a subscriber unit, a station, etc. A UE maybe a cellular phone, a personal digital assistant (PDA), a wirelessmodem, a wireless communication device, a handheld device, a laptopcomputer, a cordless phone, a wireless local loop (WLL) station, atablet, etc. A UE may be able to communicate with macro eNBs, pico eNBs,femto eNBs, relays, etc. In FIG. 1, a solid line with double arrowsindicates desired transmissions between a UE and a serving eNB, which isan eNB designated to serve the UE on the downlink and/or uplink. Adashed line with double arrows indicates interfering transmissionsbetween a UE and an eNB. For certain aspects, the UE may comprise an LTERelease 10 UE.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition the system bandwidth into multiple(K) orthogonal subcarriers, which are also commonly referred to astones, bins, etc. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (K) may bedependent on the system bandwidth. For example, K may be equal to 128,256, 512, 1024, or 2048 for system bandwidth of 1.25, 2.5, 5, 10, or 20megahertz (MHz), respectively. The system bandwidth may also bepartitioned into subbands. For example, a subband may cover 1.08 MHz,and there may be 1, 2, 4, 8, or 16 subbands for system bandwidth of1.25, 2.5, 5, 10, or 20 MHz, respectively.

FIG. 2 shows a frame structure used in LTE. The transmission timelinefor the downlink may be partitioned into units of radio frames. Eachradio frame may have a predetermined duration (e.g., 10 milliseconds(ms)) and may be partitioned into 10 subframes with indices of 0 through9. Each subframe may include two slots. Each radio frame may thusinclude 20 slots with indices of 0 through 19. Each slot may include Lsymbol periods, e.g., L=7 symbol periods for a normal cyclic prefix (asshown in FIG. 2) or L=6 symbol periods for an extended cyclic prefix.The 2L symbol periods in each subframe may be assigned indices of 0through 2L−1. The available time frequency resources may be partitionedinto resource blocks. Each resource block may cover N subcarriers (e.g.,12 subcarriers) in one slot.

In LTE, an eNB may send a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) for each cell in the eNB. Theprimary and secondary synchronization signals may be sent in symbolperiods 6 and 5, respectively, in each of subframes 0 and 5 of eachradio frame with the normal cyclic prefix, as shown in FIG. 2. Thesynchronization signals may be used by UEs for cell detection andacquisition. The eNB may send a Physical Broadcast Channel (PBCH) insymbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carrycertain system information.

The eNB may send a Physical Control Format Indicator Channel (PCFICH) inthe first symbol period of each subframe, as shown in FIG. 2. The PCFICHmay convey the number of symbol periods (M) used for control channels,where M may be equal to 1, 2, or 3 and may change from subframe tosubframe. M may also be equal to 4 for a small system bandwidth, e.g.,with less than 10 resource blocks. The eNB may send a Physical HARQIndicator Channel (PHICH) and a Physical Downlink Control Channel(PDCCH) in the first M symbol periods of each subframe (not shown inFIG. 2). The PHICH may carry information to support hybrid automaticrepeat request (HARQ). The PDCCH may carry information on resourceallocation for UEs and control information for downlink channels. TheeNB may send a Physical Downlink Shared Channel (PDSCH) in the remainingsymbol periods of each subframe. The PDSCH may carry data for UEsscheduled for data transmission on the downlink. The various signals andchannels in LTE are described in 3GPP TS 36.211, entitled “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation,” which is publicly available.

The eNB may send the PSS, SSS, and PBCH in the center 1.08 MHz of thesystem bandwidth used by the eNB. The eNB may send the PCFICH and PHICHacross the entire system bandwidth in each symbol period in which thesechannels are sent. The eNB may send the PDCCH to groups of UEs incertain portions of the system bandwidth. The eNB may send the PDSCH tospecific UEs in specific portions of the system bandwidth. The eNB maysend the PSS, SSS, PBCH, PCFICH, and PHICH in a broadcast manner to allUEs, may send the PDCCH in a unicast manner to specific UEs and may alsosend the PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period.Each resource element may cover one subcarrier in one symbol period andmay be used to send one modulation symbol, which may be a real orcomplex value. Resource elements not used for a reference signal in eachsymbol period may be arranged into resource element groups (REGs). EachREG may include four resource elements in one symbol period. The PCFICHmay occupy four REGs, which may be spaced approximately equally acrossfrequency, in symbol period 0. The PHICH may occupy three REGs, whichmay be spread across frequency, in one or more configurable symbolperiods. For example, the three REGs for the PHICH may all belong insymbol period 0 or may be spread in symbol periods 0, 1, and 2. ThePDCCH may occupy 9, 18, 32, or 64 REGs, which may be selected from theavailable REGs, in the first M symbol periods. Only certain combinationsof REGs may be allowed for the PDCCH.

A UE may know the specific REGs used for the PHICH and the PCFICH. TheUE may search different combinations of REGs for the PDCCH. The numberof combinations to search is typically less than the number of allowedcombinations for the PDCCH. An eNB may send the PDCCH to the UE in anyof the combinations that the UE will search.

FIG. 2A shows an exemplary format 200A for the uplink in LTE. Theavailable resource blocks for the uplink may be partitioned into a datasection and a control section. The control section may be formed at thetwo edges of the system bandwidth and may have a configurable size. Theresource blocks in the control section may be assigned to UEs fortransmission of control information. The data section may include allresource blocks not included in the control section. The design in FIG.2A results in the data section including contiguous subcarriers, whichmay allow a single UE to be assigned all of the contiguous subcarriersin the data section.

A UE may be assigned resource blocks in the control section to transmitcontrol information to an eNB. The UE may also be assigned resourceblocks in the data section to transmit data to the eNB. The UE maytransmit control information in a Physical Uplink Control Channel(PUCCH) 210 a, 210 b on the assigned resource blocks in the controlsection. The UE may transmit only data or both data and controlinformation in a Physical Uplink Shared Channel (PUSCH) 220 a, 220 b onthe assigned resource blocks in the data section. An uplink transmissionmay span both slots of a subframe and may hop across frequency as shownin FIG. 2A.

A UE may be within the coverage of multiple eNBs. One of these eNBs maybe selected to serve the UE. The serving eNB may be selected based onvarious criteria such as received power, pathloss, signal-to-noise ratio(SNR), etc.

A UE may operate in a dominant interference scenario in which the UE mayobserve high interference from one or more interfering eNBs. A dominantinterference scenario may occur due to restricted association. Forexample, in FIG. 1, UE 120 y may be close to femto eNB 110 y and mayhave high received power for eNB 110 y. However, UE 120 y may not beable to access femto eNB 110 y due to restricted association and maythen connect to macro eNB 110 c with lower received power (as shown inFIG. 1) or to femto eNB 110 z also with lower received power (not shownin FIG. 1). UE 120 y may then observe high interference from femto eNB110 y on the downlink and may also cause high interference to eNB 110 yon the uplink.

A dominant interference scenario may also occur due to range extension,which is a scenario in which a UE connects to an eNB with lower pathlossand lower SNR among all eNBs detected by the UE. For example, in FIG. 1,UE 120 x may detect macro eNB 110 b and pico eNB 110 x and may havelower received power for eNB 110 x than eNB 110 b. Nevertheless, it maybe desirable for UE 120 x to connect to pico eNB 110 x if the pathlossfor eNB 110 x is lower than the pathloss for macro eNB 110 b. This mayresult in less interference to the wireless network for a given datarate for UE 120 x.

In an aspect, communication in a dominant interference scenario may besupported by having different eNBs operate on different frequency bands.A frequency band is a range of frequencies that may be used forcommunication and may be given by (i) a center frequency and a bandwidthor (ii) a lower frequency and an upper frequency. A frequency band mayalso be referred to as a band, a frequency channel, etc. The frequencybands for different eNBs may be selected such that a UE can communicatewith a weaker eNB in a dominant interference scenario while allowing astrong eNB to communicate with its UEs. An eNB may be classified as a“weak” eNB or a “strong” eNB based on the received power of signals fromthe eNB received at a UE (and not based on the transmit power level ofthe eNB).

FIG. 3 is a block diagram of a design of a base station or an eNB 110and a UE 120, which may be one of the base stations/eNBs and one of theUEs in FIG. 1. For a restricted association scenario, the eNB 110 may bemacro eNB 110 c in FIG. 1, and the UE 120 may be UE 120 y. The eNB 110may also be a base station of some other type. The eNB 110 may beequipped with T antennas 334 a through 334 t, and the UE 120 may beequipped with R antennas 352 a through 352 r, where in general T≥1 andR≥1.

At the eNB 110, a transmit processor 320 may receive data from a datasource 312 and control information from a controller/processor 340. Thecontrol information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. Thedata may be for the PDSCH, etc. The transmit processor 320 may process(e.g., encode and symbol map) the data and control information to obtaindata symbols and control symbols, respectively. The transmit processor320 may also generate reference symbols, e.g., for the PSS, SSS, andcell-specific reference signal. A transmit (TX) multiple-inputmultiple-output (MIMO) processor 330 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, and/or thereference symbols, if applicable, and may provide T output symbolstreams to T modulators (MODs) 332 a through 332 t. Each modulator 332may process a respective output symbol stream (e.g., for OFDM, etc.) toobtain an output sample stream. Each modulator 332 may further process(e.g., convert to analog, amplify, filter, and upconvert) the outputsample stream to obtain a downlink signal. T downlink signals frommodulators 332 a through 332 t may be transmitted via T antennas 334 athrough 334 t, respectively.

At the UE 120, antennas 352 a through 352 r may receive the downlinksignals from the eNB 110 and may provide received signals todemodulators (DEMODs) 354 a through 354 r, respectively. Eachdemodulator 354 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 354 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 356 may obtainreceived symbols from all R demodulators 354 a through 354 r, performMIMO detection on the received symbols, if applicable, and providedetected symbols. A receive processor 358 may process (e.g., demodulate,deinterleave, and decode) the detected symbols, provide decoded data forthe UE 120 to a data sink 360, and provide decoded control informationto a controller/processor 380.

On the uplink, at the UE 120, a transmit processor 364 may receive andprocess data (e.g., for the PUSCH) from a data source 362 and controlinformation (e.g., for the PUCCH) from the controller/processor 380. Thetransmit processor 364 may also generate reference symbols for areference signal. The symbols from transmit processor 364 may beprecoded by a TX MIMO processor 366 if applicable, further processed bymodulators 354 a through 354 r (e.g., for SC-FDM, etc.), and transmittedto the eNB 110. At the eNB 110, the uplink signals from the UE 120 maybe received by the antennas 334, processed by the demodulators 332,detected by a MIMO detector 336 if applicable, and further processed bya receive processor 338 to obtain decoded data and control informationsent by the UE 120. The receive processor 338 may provide the decodeddata to a data sink 339 and the decoded control information to thecontroller/processor 340.

The controllers/processors 340 and 380 may direct the operation at theeNB 110 and the UE 120, respectively. The controller/processor 340,receive processor 338, and/or other processors and modules at the eNB110 may perform or direct operations and/or processes for the techniquesdescribed herein. The memories 342 and 382 may store data and programcodes for the eNB 110 and the UE 120, respectively. A scheduler 344 mayschedule UEs for data transmission on the downlink and/or uplink.

Example Resource Partitioning

According to certain aspects of the present disclosure, when a networksupports enhanced inter-cell interference coordination (eICIC), the basestations may negotiate with each other to coordinate resources in orderto reduce or eliminate interference by the interfering cell giving uppart of its resources. In accordance with this interferencecoordination, a UE may be able to access a serving cell even with severeinterference by using resources yielded by the interfering cell.

For example, a femto cell with a closed access mode (i.e., in which onlya member femto UE can access the cell) in the coverage area of an openmacro cell may be able to create a “coverage hole” (in the femto cell'scoverage area) for a macro cell by yielding resources and effectivelyremoving interference. By negotiating for a femto cell to yieldresources, the macro UE under the femto cell coverage area may still beable to access the UE's serving macro cell using these yieldedresources.

In a radio access system using OFDM, such as Evolved UniversalTerrestrial Radio Access Network (E-UTRAN), the yielded resources may betime based, frequency based, or a combination of both. When thecoordinated resource partitioning is time based, the interfering cellmay simply not use some of the subframes in the time domain. When thecoordinated resource partitioning is frequency based, the interferingcell may yield subcarriers in the frequency domain. With a combinationof both frequency and time, the interfering cell may yield frequency andtime resources.

FIG. 4 illustrates an example scenario where eICIC may allow a macro UE120 y supporting eICIC (e.g., a Rel-10 macro UE as shown in FIG. 4) toaccess the macro cell 110 c even when the macro UE 120 y is experiencingsevere interference from the femto cell y, as illustrated by the solidradio link 402. A legacy macro UE 120 u (e.g., a Rel-8 macro UE as shownin FIG. 4) may not be able to access the macro cell 110 c under severeinterference from the femto cell 110 y, as illustrated by the brokenradio link 404. A femto UE 120 v (e.g., a Rel-8 femto UE as shown inFIG. 4) may access the femto cell 110 y without any interferenceproblems from the macro cell 110 c.

According to certain aspects, networks may support eICIC, where theremay be different sets of partitioning information. A first of these setsmay be referred to as Semi-static Resource Partitioning Information(SRPI). A second of these sets may be referred to as Adaptive ResourcePartitioning Information (ARPI). As the name implies, SRPI typicallydoes not change frequently, and SRPI may be sent to a UE so that the UEcan use the resource partitioning information for the UE's ownoperations.

As an example, the resource partitioning may be implemented with 8 msperiodicity (8 subframes) or 40 ms periodicity (40 subframes). Accordingto certain aspects, it may be assumed that frequency division duplexing(FDD) may also be applied such that frequency resources may also bepartitioned. For communications via the downlink (e.g., from a cell nodeB to a UE), a partitioning pattern may be mapped to a known subframe(e.g., a first subframe of each radio frame that has a system framenumber (SFN) value that is a multiple of an integer N, such as 4). Sucha mapping may be applied in order to determine resource partitioninginformation (RPI) for a specific subframe. As an example, a subframethat is subject to coordinated resource partitioning (e.g., yielded byan interfering cell) for the downlink may be identified by an index:Index_(SRPI_DL)=(SFN*10+subframe number)mod 8

For the uplink, the SRPI mapping may be shifted, for example, by 4 ms.Thus, an example for the uplink may be:Index_(SRPI_UL)=(SFN*10+subframe number+4)mod 8

SRPI may use the following three values for each entry:

U (Use): this value indicates the subframe has been cleaned up from thedominant interference to be used by this cell (i.e., the maininterfering cells do not use this subframe);

N (No Use): this value indicates the subframe shall not be used; and

X (Unknown): this value indicates the subframe is not staticallypartitioned. Details of resource usage negotiation between base stationsare not known to the UE.

Another possible set of parameters for SRPI may be the following:

U (Use): this value indicates the subframe has been cleaned up from thedominant interference to be used by this cell (i.e., the maininterfering cells do not use this subframe);

N (No Use): this value indicates the subframe shall not be used;

X (Unknown): this value indicates the subframe is not staticallypartitioned (and details of resource usage negotiation between basestations are not known to the UE); and

C (Common): this value may indicate all cells may use this subframewithout resource partitioning. This subframe may be subject tointerference, so that the base station may choose to use this subframeonly for a UE that is not experiencing severe interference.

The serving cell's SRPI may be broadcasted over the air. In E-UTRAN, theSRPI of the serving cell may be sent in a master information block(MIB), or one of the system information blocks (SIBs). A predefined SRPImay be defined based on the characteristics of cells, e.g. macro cell,pico cell (with open access), and femto cell (with closed access). Insuch a case, encoding of SRPI in the system overhead message may resultin more efficient broadcasting over the air.

The base station may also broadcast the neighbor cell's SRPI in one ofthe SIBs. For this, SRPI may be sent with its corresponding range ofphysical cell identifiers (PCIs).

ARPI may represent further resource partitioning information with thedetailed information for the ‘X’ subframes in SRPI. As noted above,detailed information for the ‘X’ subframes is typically only known tothe base stations, and a UE does not know it.

FIGS. 5 and 6 illustrate examples of SRPI assignment in the scenariowith macro and femto cells. A U, N, X, or C subframe is a subframecorresponding to a U, N, X, or C SRPI assignment.

FIG. 7 is a diagram 700 illustrating a range expanded cellular region ina heterogeneous network. A lower power class eNB such as the RRH 710 bmay have a range expanded cellular region 703 that is expanded from thecellular region 702 through enhanced inter-cell interferencecoordination between the RRH 710 b and the macro eNB 710 a and throughinterference cancelation performed by the UE 720. In enhanced inter-cellinterference coordination, the RRH 710 b receives information from themacro eNB 710 a regarding an interference condition of the UE 720. Theinformation allows the RRH 710 b to serve the UE 720 in the rangeexpanded cellular region 703 and to accept a handoff of the UE 720 fromthe macro eNB 710 a as the UE 720 enters the range expanded cellularregion 703.

FIG. 8 is a diagram illustrating a network 800, which includes a macronode and a number of remote radio heads (RRHs) in accordance withcertain aspects of the present disclosure. The macro node 802 isconnected to RRHs 804, 806, 808, 810 with optical fiber. In certainaspects, network 800 may be a homogeneous network or a heterogeneousnetwork and the RRHs 804-810 may be low power or high power RRHs. In anaspect, the macro node 802 handles all scheduling within the cell, foritself and the RRHs. The RRHs may be configured with the same cellidentifier (ID) as the macro node 802 or with different cell IDs. If theRRHs are configured with the same cell ID, the macro node 802 and theRRHs may operate as essentially one cell controlled by the macro node802. On the other hand, if the RRHs and the macro node 802 areconfigured with different cell IDs, the macro node 802 and the RRHs mayappear to a UE as different cells, though all control and scheduling maystill remain with the macro node 802. It should further be appreciatedthat the processing for the macro node 802 and the RRHs 804, 806, 808,810 may not necessarily have to reside at the macro node. It may also beperformed in a centralized fashion at some other network device orentity that is connected with the macro and the RRHs.

As used herein, the term transmission/reception point (“TxP”) generallyrefers geographically separated transmission/reception nodes controlledby at least one central entity (e.g., eNodeB), which may have the sameor different cell IDs.

In certain aspects, when each of the RRHs share the same cell ID withthe macro node 802, control information may be transmitted using CRSfrom the macro node 802 or both the macro node 802 and all of the RRHs.The CRS is typically transmitted from each of the transmission pointsusing the same resource elements, and therefore the signals collide.When each of the transmission points has the same cell ID, CRStransmitted from each of the transmission points may not bedifferentiated. In certain aspects, when the RRHs have different cellIDs, the CRS transmitted from each of the TxPs using the same resourceelements may or may not collide. Even in the case, when the RRHs havedifferent cell IDs and the CRS collide, advanced UEs may differentiateCRS transmitted from each of the TxPs using interference cancellationtechniques and advanced receiver processing.

In certain aspects, when all transmission points are configured with thesame cell ID and CRS is transmitted from all transmission points, properantenna virtualization is needed if there are an unequal number ofphysical antennas at the transmitting macro node and/or RRHs. That is,CRS is to be transmitted with an equal number of CRS antenna ports. Forexample, if the node 802 and the RRHs 804, 806, 808 each have fourphysical antennas and the RRH 810 has two physical antennas, a firstantenna of the RRH 810 may be configured to transmit using two CRS portsand a second antenna of the RRH 810 may be configured to transmit usinga different two CRS ports. Alternatively, for the same deployment, macro802 and RRHs 804, 806, 808, may transmit only two CRS antenna ports fromselected two out of the four transmit antennas per transmission point.Based on these examples, it should be appreciated that the number ofantenna ports may be increased or decreased in relation to the number ofphysical antennas.

As discussed supra, when all transmission points are configured with thesame cell ID, the macro node 802 and the RRHs 804-810 may all transmitCRS. However, if only the macro node 802 transmits CRS, outage may occurclose to an RRH due to automatic gain control (AGC) issues. In such ascenario, CRS based transmission from the macro 802 may be received atlow receive power while other transmissions originating from theclose-by RRH may be received at much larger power. This power imbalancemay lead to the aforementioned AGC issues.

In summary, typically, a difference between same/different cell IDsetups relates to control and legacy issues and other potentialoperations relying on CRS. The scenario with different cell IDs, butcolliding CRS configuration may have similarities with the same cell IDsetup, which by definition has colliding CRS. The scenario withdifferent cell IDs and colliding CRS typically has the advantagecompared to the same cell ID case that system characteristics/componentswhich depend on the cell ID (e.g., scrambling sequences, etc.) may bemore easily differentiated.

The exemplary configurations are applicable to macro/RRH setups withsame or different cell IDs. In the case of different cell IDs, CRS maybe configured to be colliding, which may lead to a similar scenario asthe same cell ID case but has the advantage that system characteristicswhich depend on the cell ID (e.g., scrambling sequences, etc.) may bemore easily differentiated by the UE).

In certain aspects, an exemplary macro/RRH entity may provide forseparation of control/data transmissions within the transmission pointsof this macro/RRH setup. When the cell ID is the same for eachtransmission point, the PDCCH may be transmitted with CRS from the macronode 802 or both the macro node 802 and the RRHs 804-810, while thePDSCH may be transmitted with channel state information reference signal(CSI-RS) and demodulation reference signal (DM-RS) from a subset of thetransmission points. When the cell ID is different for some of thetransmission points, PDCCH may be transmitted with CRS in each cell IDgroup. The CRS transmitted from each cell ID group may or may notcollide. UEs may not differentiate CRS transmitted from multipletransmission points with the same cell ID, but may differentiate CRStransmitted from multiple transmission points with different cell IDs(e.g., using interference cancellation or similar techniques).

In certain aspects, in the case where all transmission points areconfigured with the same cell ID, the separation of control/datatransmissions enables a UE transparent way of associating UEs with atleast one transmission point for data transmission while transmittingcontrol based on CRS transmissions from all the transmission points.This enables cell splitting for data transmission across differenttransmission points while leaving the control channel common. The term“association” above means the configuration of antenna ports for aspecific UE for data transmission. This is different from theassociation that would be performed in the context of handover. Controlmay be transmitted based on CRS as discussed supra. Separating controland data may allow for a faster reconfiguration of the antenna portsthat are used for a UE's data transmission compared to having to gothrough a handover process. In certain aspects, cross transmission pointfeedback may be possible by configuring a UE's antenna ports tocorrespond to the physical antennas of different transmission points.

In certain aspects, UE-specific reference signals enable this operation(e.g., in the context of LTE-A, Rel-10 and above). CSI-RS and DM-RS arethe reference signals used in the LTE-A context. Interference estimationmay be carried out based on or facilitated by CSI-RS muting. Whencontrol channels are common to all transmission points in the case of asame cell ID setup, there may be control capacity issues because PDCCHcapacity may be limited. Control capacity may be enlarged by using FDMcontrol channels. Relay PDCCH (R-PDCCH) or extensions thereof, such asan enhanced PDCCH (ePDCCH) may be used to supplement, augment, orreplace the PDCCH control channel.

Power Control and User Multiplexing for CoMP

Various techniques have been considered for joint processing acrossheterogeneous networks coordinated multipoint (HetNet CoMP) eNBs. Forexample, within a macro cell coverage, multiple remote radio heads(RRHs) may be deployed to enhance capacity/coverage of a network. Asdiscussed above, these RRHs may have a same cell ID as the macro cell,such that a single frequency network (SFN) is formed for downlink (DL)transmission. However, many issues may be encountered in the uiplink(UL) for such a HetNet CoMP scheme. One problem may be that with a samephysical cell identifier (PCI) for all cells, only one common referencesignal power spectral density (CRS PSD) may be broadcasted. However, RRHand macro cell may have 16-20 dB power difference. This mismatch maylead to a large error in open loop power control (OL PC). Anotherproblem may be that if only the macro cell transmits CRS, and no RRHstransmit CRS, a UE close to an RRH may transmit a very large UL signalto jam the reception for the RRH. These problems may lead to performancedegradations.

The following disclosure discusses various ways to improve UL powercontrol for different HetNet CoMP scenarios. In addition, various ULCoMP receiver and processing options, and UL channel configurationoptions are also discussed.

In certain aspects, various eNB power classes may be defined in HetNetCoMP. For example, macro cells with 46 dBm (nominal), pico cells with 30dBm (nominal), or 23 and 37 dBm, RRH with 30 dBm (nominal) or 37 dBmpossible, and Femto cells with 20 dBm (nominal).

A pico cell typically has its own physical cell identifier (PCI), mayhave X2 connection with a macro cell, may have own scheduler operation,and may link to multiple macro cells. An RRH may or may not have a samePCI as macro cell, may have fiber connection with the macro cell, andmay have its scheduling performed only at the macro cell. A femto cellmay have restricted association and is typically not considered for CoMPschemes.

UL CoMP Processing

In certain aspects, various CoMP processing schemes may be defined whenall cells or a subset of cells receive UL data, control and soundingreference signal (SRS).

In a first aspect, macro diversity reception may be defined for a subsetof cells. For this aspect, whichever of the subset of cells successfullydecodes the UL reception, may forward a decision to the serving cell.

In a second aspect, joint processing may be defined by combining loglikelihood ratio (LLR) from a subset of cells. In this aspect, there maybe a need to move LLRs to the serving cell.

In a third aspect, joint multi-user detection may be defined. This mayinclude using different cyclic shifts/Walsh codes among users within alarge macro/RRH region to separate users' channel(s). In an aspect,interference cancellation (IC) may be carried out for interfering usersamong all cells since all information is shared among all cells. Inanother aspect, data separation may be defined by spatial divisionmultiple access SDMA, UL MU-MIMO etc.

In a fourth aspect, UL CoMP with Rel-11 UEs may be defined. In thisaspect, MIMO/beamforming (BF) may be based on the SRS channeltransmitted from multiple antennas. Further, precoding matrix selectionmay be chosen by the serving eNB based on SRS. Also, joint processingmay be performed from multiple UL cells. In an aspect, code book designmay be reused for UL since they are transmitter (Tx) driven.

UL Power Control

In certain aspects, for HetNet CoMP schemes where the macro cell and oneor more RRHs share a same PCI, two scenarios may exist. In a firstscenario, only the macro cell may transmit the CRS, PSS, SSS and/orPBCH. In an alternate scenario, both macro and RRHs may transmit theCRS, PSS, SSS and/or PBCH.

FIG. 9 illustrates an example scenario 900 for HetNet CoMP where onlythe macro cell transmits a common reference signal (CRS) in accordancewith certain aspects of the present disclosure. The heterogeneousnetwork of FIG. 9 includes eNB0 associated with a macro cell andmultiple RRHs that may be associated with pico cells including RRH1,RRH2 and RRH3. The RRHs 1, 2 and 3 may be connected with the eNB0 viaoptical fiber cables. UE 120 may communicate with the eNB0 as well asthe RRHs 1, 2, and 3. eNB0 may transmit the CRS while the RRHs remainsilent. In certain aspects, for DL, control may be based on the macrocell and data may be based on SFN from all cells (including macro andpico cells) or a subset of cells with UE-reference signals (RS) fordownlink. On the other hand, for UL, both control and data may bereceived on multiple cells (e.g. eNB0 as well as one or more RRHs).

In certain aspects, with DL CRS measurement from one cell (e.g. eNB0)and UL reception from multiple cells (RRHs 1, 2 and 3), open loop powercontrol (OL PC) may be inaccurate since DL path loss (PL) may bemeasured at the UE 120 based on CRS from the macro cell (eNB0) only. Inthis scenario, OL PC may be accurate if UL is received by macro cellonly.

Various power control options may be defined to address this problem.For example, in a first aspect, additional back off/reduction oftransmit power from the UE 120 may be defined in OL PC algorithm to takeinto account the UL macro diversity gain or joint processing gain due toprocessing of UL signals by a plurality of transmission points. Thisadditional reduction in transmit power of the UE may be signaled fromeNB0 to the UE 120, for example to adjust P0 factor. In certain aspects,the P0 factor defines a target received power at the eNB0 for a randomaccess channel (RACH) that is set to a low value to allow low initialtransmit power of the RACH. In an aspect, the P0 factor is determinedand/or signaled to adjust the OL PC based on differences between pathloss between the UE and one or more transmission points involved in DLCoMP operations and one or more transmission points involved in UL CoMPoperations. In an aspect, eNB may also signal one or more parametersthat represents a path loss difference between DL and UL serving nodes,which may be used by the UE in OL PC. In certain aspects, this methodmay be applicable to CoMP operations involving different DL transmissionpoints and UL reception points.

In a second aspect, closed loop power control may be performed based onSRS transmitted from the UE 120. In an aspect, joint processing of theSRS may be carried out by the same cooperating cells as used for data.The closed loop PC may be based on the SRS channel signal to noise ratio(SNR) with an offset between PUSCH and SRS.

In a third aspect, a slow start random access channel RACH transmitpower may be defined so that it will not jam the close by cells.

FIG. 10 illustrates example operations 1000, performed at a basestation, for uplink power control, in accordance with certain aspects ofthe disclosure. Operations 1000 may be executed, for example atprocessor(s) 330 and/or 340 of the eNB 110. Operations 1000 being, at1002, by determining one or more parameters for use by a UE in OL PC,wherein the one or more parameters are determined to take into accountCoMP operations. At 1004, the one or more parameters may be signaled tothe UE.

The operations 1000 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 10. For example, operations 1000 illustrated in FIG.10 correspond to components 1000A illustrated in FIG. 10A. In FIG. 10A,a parameter determiner 1002A may determine one or more parameters foruse by a UE 120 in OL PC. A transmitter 1004A may transmit the one ormore parameters to the UE 120.

In certain aspects, when UE 120 is close to an RRH (e.g. RRH 1, 2 or 3having common cell ID), it may have large DL path loss from the eNB0,but a small path loss to the close by RRH. In this scenario, ULtransmission based on OL PC may jam the RRH. Thus, a UE 120 close to anRRH, which is not transmitting CRS and is far away from the eNB0 mayhave very high signal power to jam the RRH based on the OL PC.

Various power control options may be defined to address this problem. Ina first aspect, OL PC may be performed based on CSI-RS instead of CRS.In an aspect, a different CSI-RS may be transmitted from eachtransmission point and the UE 120 may perform OL PC based on a strongestCSI-RS. In a second aspect, noise padding may be carried at the RRH. Incertain aspects, the UE may receive signaling indicating at least one oflocation or power spectrum density (PSD) of CSI-RS for each of a set oftransmission points. In an aspect, the signaling may be conveyed to theUE in a system information block (SIB).

FIG. 11 illustrates example operations 1100, performed by a UE, foruplink power control to avoid jamming a close by RRH, in accordance withcertain aspects of the present disclosure. Operations 1100 may beexecuted, for example at processor(s) 358 and/or 380 of the UE 120.Operations 1100 may being, at 1102, by measuring CSI-RS transmitted fromat least one of a set of transmission points involved in CoMP operationswith the UE. At 1104, OL PC may be performed based on the measuredCSI-RS from at least one of the transmission points.

The operations 1100 may be performed by any suitable components or othermeans capable of performing the corresponding functions of FIG. 11. Forexample, the operations 1100 illustrated in FIG. 11 correspond tocomponents 1100A illustrated in FIG. 11A.

FIG. 12 illustrates an example scenario 1200 for HetNet CoMP where bothmacro and pico cells transmit a same CRS in accordance with certainaspects of the present disclosure. The heterogeneous network of FIG. 12includes eNB0 (P0) associated with a macro cell and multiple RRHsassociated with pico cells including RRH1 (P1), RRH2 (P2) and RRH3 (P3).eNB0 and the RRHs may communicate with UE 120. As noted above the RRHsmay be connected with eNB0 via fiber optic cables. In this scenario,both eNB0 and the RRHs may transmit the same CRS. In certain aspects,for DL, both control and data may be based on SFN from all cells and adata channel may have additional beam-forming with UE-RS. Further, forUL, both the control and data may be received on multiple cells(diversity or joint processing on UL).

In certain aspects, only one reference signal power spectral density (RSPSD) level may be advertized in this scenario, but eNB0 and RRH may havedifferent RS levels, which may lead to a mismatch in RS power levels.That is, the DL SFN transmission from different transmission points maypossibly be with different PSD levels of CRS and the UE 120 and may notbe able to differentiate CRS level from path loss (PL) difference. Forexample, for P1 and P2 with path losses PL1 and PL2, the received signalon DL may be R1=P1*PL1+P2*PL2, and the received signal on the UL isR2=P(PL1+PL2). Thus, the measured may not be reciprocal between DL andUL.

The mismatch in the DL RS levels at the UE 120, transmitted fromdifferent transmission points may be addressed in various ways. In afirst aspect, CRS PSD level from all cells may be maintained at a samelevel so that DL PL may be applied to UL PL. This may however beunlikely due to the Macro/Pico/RRH power difference.

In a second aspect, macro and RRH may send different system informationblock 1 (SIB1) with different PDCCH. SIB1 from macro and RRH may betransmitted in different frequency locations as indicated by PDCCH. TheUE 120 may detect both PDCCH and both SIB1. SIB1 from Macro/RRH maycontain CRS or CSI-RS level from Macro/RRH. From PDCCH and SIB1 signalstrength, UE 120 may determine which cell is the strongest DL cell andapply open loop power control based on the strongest DL as well as itsCRS or CSI-RS level.

In a third aspect, macro eNB0 may advertize two sets of information inits system information block (SIB). One, positions of all cellsincluding Macro eNB0 and RRH {x0, x1, x2, . . . xn}, and two, PSD of CRSor CSI-RS of all cells including macro eNB0 and RRH in the same order{p0, p1, . . . , pn}. In an aspect, from positions of the cell as wellits own GPS location, UE 120 may find the distance from each of thecells and perform random access channel (RACH) procedure to either theclosest cell or to the cell with the smallest path loss. In an aspect,from all the information above and with the received signal strength,the UE 120 may calculate approximate path loss from each of the cells.

In certain aspects, when the macro eNB0 and the pico RRHs transmit asame CRS, DL PL measurement may be based on the SFN from all cells.However, UL transmission may only be based on diversity or jointprocessing from a subset of cells. This may lead to a mismatch betweenDL and UL processing. This problem may be addressed in various ways.

In a aspects, transmit power based on open loop power control may beadjusted depending on the difference between the DL transmission cellsand the UL reception cells.

In certain aspects, PL calculation may be based on CSI-RS which may beunique from each cell, and the OL PC and closed loop PC may take intoaccount participating UL CoMP cells.

UL Multiplexing

In certain aspects, both DL CoMP and UL CoMP grouping may depend onaccurate sounding of the channel. For an RRH with the same PCI as macroeNB, there may be no differentiation of CSI-RS and SRS from differentRRH. In certain aspects, to address this issue, for both CSI-RS and SRS,the configuration/scrambling etc may be decoupled from the common PCIthat the RRH may have.

In an aspect, for DL CoMP, different CSI-RS may be transmitted fromdifferent cells, even when a same PCI is used in the different RRHs.FIG. 13 illustrates example operations 1300, performed by a basestation, for grouping of cells associated with DL CoMP, in accordancewith certain aspects of the present disclosure. Operations 1300 may beexecuted for example at processor(s) 330, 338 and/or 340 of the eNB 110.

Operations 1300 may begin, at 1302, by determining a channel stateinformation reference signal (CSI-RS), the CSI-RS being different fromCSI-RS transmitted by one or more other transmission points sharing acommon physical cell identifier (PCI) with the base station, the CSI-RSbeing decoupled from the PCI. At 1304, the CSI-RS is transmitted fromthe base station. In certain aspects, CSI-RS configuration comprises aCSI-RS sequence and a frequency location.

The operations 1300 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 13. For example, operations 1300 illustrated in FIG.13 correspond to components 1300A illustrated in FIG. 13A. In FIG. 13A,a CSI-RS determiner 1302A may determine a CSI-RS and a transmitter 1304Amay transmit the CSI-RS.

In an aspect, for UL CoMP, different SRS may be transmitted fromdifferent UEs, including UEs in proximity to RRHs with a same PCI. Oneor more transmission points receiving the different SRS may determine agrouping of cells for UL CoMP for a UE based on SRS transmitted by oneor more UEs, and transmit the grouping to the UEs.

FIG. 14 illustrates example operations 1400, performed by a UE, forgrouping of cells associated with UL CoMP, in accordance with certainaspects of the present disclosure. Operations 1400 may be executed, forexample at processor(s) 358, 364 and/or 380.

Operations 1400 may begin, at 1402, by transmitting a sounding referencesignal (SRS) from the UE in proximity to a plurality of transmissionpoints sharing a common physical cell identifier (PCI). At 1404,information may be received, from at least one of the transmissionpoints, regarding configuration for uplink coordinated multipoint (ULCoMP) operation, the configuration being decoupled from the PCI.

The operations 1400 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 14. For example, operations 1400 illustrated in FIG.14 correspond to components 1400A illustrated in FIG. 14A. In FIG. 14A,the transmitter 1402A may transmit an SRS from the UE 120 and thereceiver 1404A may receive information regarding configuration for ULCoMP from at least one eNB 110. The transmitted SRS and the received ULCoMP configuration may be processed at processor 358/364/380.

In certain aspects, current SRS separation is provided by root sequence,cyclic shift, frequency location, and comb, where root sequence is PCIdependent. In an aspect, for RRHs with the same PCI, root sequenceselection may be increased and multiple roots may be used within thesame macro/RRH region.

In certain aspect, for CSI-RS based CoMP grouping, where a jointprocessing/Macro diversity group is determined based on DL CSI-RS, eachcell may transmit distinct CSI-RS pattern as noted above. In an aspect,the UE may determine and/or select both DL CoMP cells as well as UL CoMPcells based on a received signal strength of the CSI-RS from each cell.In an aspect, this selection of UL CoMP cells may be fed back to servingeNB. Alternatively, PL from each cell, calculated based on the CSI-RS,may be fed back to the serving eNB and the serving eNB may make the ULCoMP decision. Also, there may be a need to offset the difference intransmit power when deciding on the UL CoMP, so that UL CoMP is strictlybased on PL from different cells.

In certain aspects, for SRS based UL CoMP grouping, where a jointprocessing/macro diversity group is determined based on SRS, the UE maytransmit SRS (as noted above), and a group of cells with strong SRSreceived signal may participate in UL joint processing.

FIG. 15 illustrates example operations 1500, performed by a UE, forgrouping of cells associated with CoMP, in accordance with certainaspects of the present disclosure. Operations 1500 may be executed, forexample at processor(s) 358, 364 and/or 380.

Operations 1500 may being, at 1502, by receiving distinct CSI-RStransmitted from a plurality of cells. At 1504, a feedback may betransmitted based on the received CSI-RS, that may be used to determineone or more cells to include in a UL CoMP group.

The operations 1500 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 15. For example, operations 1500 illustrated in FIG.15 correspond to components 1500A illustrated in FIG. 15A. In FIG. 15A,a receiver 1502A may receive CSI-RS transmitted from a plurality ofcells (e.g eNB 110) and a transmitter 1504A may transmit feedback basedon the received CSI-RS. A processor 358/364/380 may process the receivedCSI-RS and the feedback to be transmitted from the UE 120.

FIG. 16 illustrates example operations 1600, performed by a basestation, for grouping of cells associated with UL CoMP, in accordancewith certain aspects of the present disclosure. Operations 1600 may beexecuted for example at processor(s) 330, 338 and/or 340 of the eNB 110.

Operations 1600 may being, at 1602, by receiving a transmission from aUE. At 1604, one or more cells may be determined to include in a CoMPgroup, based on the received transmission.

The operations 1600 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 16. For example, operations 1600 illustrated in FIG.16 correspond to components 1600A illustrated in FIG. 16A. In FIG. 16A,a receiver 1602A may receive a transmission from a UE and a UL CoMPgroup determiner 1604A may determine one or more cells to include in aUL CoMP group, based on the received transmission.

PUCCH Transmission/Reception Options

In certain aspects, localized transmission may be made to every one'sclosest cell. This aspect may include separate PUCCH configuration fromPCI. Each cell may have an option to signal its own users about thechannel quality indication (CQI) configuration for CQI transmission.Further, CQI pool may be increased by allowing different CGS amongdifferent RRH and macro even with the same PCI.

FIG. 17 illustrates example operations 1700, by a transmission pointinvolved in CoMP operations, in accordance with certain aspects of thepresent disclosure. Operations 1700 may be executed for example atprocessor(s) 330, 338 and/or 340 of the eNB 110.

Operations 1700 may begin, at 1702, by determining channel qualityindication (CQI) configuration for CQI transmission by one or more UEs.At 1704, the one or more UEs may be signaled the CQI configuration forthe CQI transmission, wherein the signaled CQI configuration isdecoupled from physical cell identifier (PCI) of the transmission point.

The operations 1700 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 17. For example, operations 1700 illustrated in FIG.17 correspond to components 1700A illustrated in FIG. 17A. In FIG. 17A,a CQI configuration determiner 1702A may determine CQI configuration forCQI transmission by one or more UEs. A transmitter 1704A may signal oneor more UEs regarding the CQI configuration for the CQI transmission.

In certain aspects, transmission may be made to multiple participatingcells. In this aspect, one anchor cell may be responsible to signal thePUCCH configuration. Further, this aspect may include separate controlchannel reception region from data channel reception. For example, areduced CoMP group for PUCCH may reduce processing load. Also, forexample, larger PUCCH CoMP group comparing to PUSCH due to lesstransfer.

FIG. 18 illustrates example operations 1800, by a transmission pointinvolved in CoMP operations, in accordance with certain aspects of thepresent disclosure. Operations 1800 may be executed for example atprocessor(s) 330, 338 and/or 340 of the eNB 110.

Operations 1800 may being, at 1802, by receiving a physical uplinkcontrol channel (PUCCH) configuration from a first transmission pointparticipating in coordinated multipoint (CoMP) operations with one ormore other transmission points. At 1804, a PUCCH may be transmitted to afirst set of one or more transmission points in accordance with thePUCCH configuration. At 1806, a PUSCH may be transmitted to a second setof one or more transmission points different from than the first set oftransmission points.

The operations 1800 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 18. For example, operations 1800 illustrated in FIG.18 correspond to components 1800A illustrated in FIG. 18A. In FIG. 18A,a receiver 1802A may receive a physical uplink control channel (PUCCH)configuration from a first transmission point. A transmitter 1804A/1806Amay transmit a PUCCH to a first set of one or more transmission pointsand may transmit a PUSCH to a second set of one or more transmissionpoints.

In certain aspects, CQI content may be reporting the DL signal qualityfrom M cells. CQI uplink transmission may be received from N cells. Thisaspect may include separate CQI reporting DL cell set from CQIconfiguration for UL cell set.

FIG. 19 illustrates example operations 1900, performed by a UE involvedin CoMP operations, in accordance with certain aspects of the presentdisclosure. Operations 1900 may be executed, for example at processor(s)358, 364 and/or 380.

Operations 1900 may being, at 1902, by generating CQI information fordownlink transmission from a first set of one or more transmissionpoints involved in CoMP operations with the UE. At 1904, the CQIinformation may be sent to a second set of transmission points involvedin CoMP operations with the UE.

The operations 1900 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 19. For example, operations 1900 illustrated in FIG.19 correspond to components 1900A illustrated in FIG. 19A. In FIG. 19A,a CQI generator 1902A may generate CQI for downlink transmission from afirst set of one or more transmission points involved in CoMP operationswith the UE. A transmitter 1904A may transmit the CQI information to asecond set of transmission points involved in CoMP operations with theUE.

In certain aspects, frequency division multiplexing (FDM) of PUCCHbetween Macro and RRH, may schedule data into PUCCH region for interiorusers.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and/or write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal. Generally, where there are operations illustrated inFigures, those operations may have corresponding counterpartmeans-plus-function components with similar numbering.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein, but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communications by a user equipment (UE), comprising: measuring channel state information reference signals (CSI-RS) transmitted from at least one of a set of transmission points involved in coordinated multipoint (CoMP) operations with the UE, wherein the measurement of the CSI-RS comprises measuring the CSI-RS transmitted from each of the set of transmission points; and performing open loop power control based on the measured CSI-RS from the at least one of the transmission points, the open loop power control being based on the strongest of the measured CSI-RSs.
 2. The method of claim 1, wherein the CSI-RS transmitted from each of the set of transmission points is different.
 3. The method of claim 2, wherein a common cell ID is used for each of the set of transmission points.
 4. The method of claim 1, further comprising receiving signaling indicating at least one of location or power spectrum density (PSD) of CSI-RS for each of the set of transmission points.
 5. The method of claim 4, wherein the signaling is conveyed in a system information block (SIB).
 6. An apparatus for wireless communications, comprising: means for measuring channel state information reference signals (CSI-RS) transmitted from at least one of a set of transmission points involved in coordinated multipoint (CoMP) operations with a user-equipment (UE), wherein the means for measuring of the CSI-RS comprises means for measuring the CSI-RS transmitted from each of the set of transmission points; and means for performing open loop power control based on the measured CSI-RS from the at least one of the transmission points, the means for performing the open loop power control being based on the strongest of the measured CSI-RSs.
 7. The apparatus of claim 6, wherein the CSI-RS transmitted from each of the set of transmission points is different.
 8. The apparatus of claim 7, wherein a common cell ID is used for each of the set of transmission points.
 9. The apparatus of claim 6, further comprising means for receiving signaling indicating at least one of location or power spectrum density (PSD) of CSI-RS for each of the set of transmission points.
 10. The apparatus of claim 9, wherein the signaling is conveyed in a system information block (SIB).
 11. An apparatus for wireless communications, comprising: at least one processor configured to: measure channel state information reference signals (CSI-RS) transmitted from at least one of a set of transmission points involved in coordinated multipoint (CoMP) operations with a UE, wherein the measurement of the CSI-RS comprises measuring the CSI-RS transmitted from each of the set of transmission points; and perform open loop power control based on the measured CSI-RS from the at least one of the transmission points, the open loop power control being based on the strongest of the measured CSI-RSs; and a memory coupled to the at least one processor.
 12. A computer-program product for wireless communications, comprising a non-transitory computer-readable medium having code, that when executed by a processor, performs: measuring channel state information reference signals (CSI-RS) transmitted from at least one of a set of transmission points involved in coordinated multipoint (CoMP) operations with a UE, wherein the measurement of the CSI-RS comprises measuring the CSI-RS transmitted from each of the set of transmission points; and performing open loop power control based on the measured CSI-RS from the at least one of the transmission points, the open loop power control being based on the strongest of the measured CSI-RSs.
 13. A method for wireless communications by a base station, comprising: determining one or more parameters for use by a user equipment (UE) in open loop (OL) power control, wherein the one or more parameters are determined to take into account coordinated multipoint (CoMP) operations, wherein the one or more parameters are determined to take into account at least one of uplink (UL) macro diversity gain or joint processing gain; and signaling the one or more parameters to the UE.
 14. The method of claim 13, wherein the CoMP operations comprise different DL transmission points and UL reception points.
 15. The method of claim 13, wherein at least one of the one or more parameters comprises a parameter representing a target power received at the base station for a random access channel (RACH) that is set to a low value to allow low initial transmit power of the RACH.
 16. The method of claim 13, wherein the one or more parameters are determined to adjust open loop power control based on differences between path loss between the UE and one or more transmission points involved in downlink (DL) CoMP operations and one or more transmission points involved in uplink (UL) CoMP operations.
 17. The method of claim 13, wherein the one or more parameters comprise a parameter that represents path loss difference between DL and UL serving nodes.
 18. An apparatus for wireless communications, comprising: means for determining one or more parameters for use by a user equipment (UE) in open loop (OL) power control, wherein the one or more parameters are determined to take into account coordinated multipoint (CoMP) operations, wherein the one or more parameters are determined to take into account at least one of uplink (UL) macro diversity gain or joint processing gain; and means for signaling the one or more parameters to the UE.
 19. The apparatus of claim 18, wherein the COMP operations comprise different DL transmission points and UL reception points.
 20. The apparatus of claim 18, wherein at least one of the one or more parameters comprises a parameter representing a target power received at a base station for a random access channel (RACH) that is set to a low value to allow low initial transmit power of the RACH.
 21. The apparatus of claim 18, wherein the one or more parameters are determined to adjust open loop power control based on differences between path loss between the UE and one or more transmission points involved in downlink (DL) CoMP operations and one or more transmission points involved in uplink (UL) CoMP operations.
 22. The apparatus of claim 18, wherein the one or more parameters comprise a parameter that represents path loss difference between DL and UL serving nodes.
 23. An apparatus for wireless communications, comprising: at least one processor configured to: determine one or more parameters for use by a user equipment (UE) in open loop (OL) power control, wherein the one or more parameters are determined to take into account coordinated multipoint (ColVIP) operations, wherein the one or more parameters are determined to take into account at least one of uplink (UL) macro diversity gain or joint processing gain; and signal the one or more parameters to the UE; and a memory coupled to the at least one processor.
 24. A computer-program product for wireless communications, comprising a non-transitory computer-readable medium comprising code, that when executed by a processor, performs: determining one or more parameters for use by a user equipment (UE) in open loop (OL) power control, wherein the one or more parameters are determined to take into account coordinated multipoint (CoMP) operations, wherein the one or more parameters are determined to take into account at least one of uplink (UL) macro diversity gain or joint processing gain; and signaling the one or more parameters to the UE. 